Have |CreateSelfSignedCert| take an |EVP_PKEY|.

That's what it actually uses internally and, with this change, it's
possible to also create ECDSA certificates.

TBR=mnissler,sergeyu

Change-Id: I675ad79614a21322110cb6ebd0444fe41641e03f
Reviewed-on: https://chromium-review.googlesource.com/971829
Commit-Queue: Adam Langley <[email protected]>
Reviewed-by: David Benjamin <[email protected]>
Cr-Commit-Position: refs/heads/master@{#544539}
7 files changed